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Poster presentation

We investigate a functional role and cause for the neural variability in the integrated
population response of the linear component of the Horizontal Vestibulo-Ocular Reflex
(VOR), specifically looking at the role and function of noise and neural heterogeneity
in this system.

The linear component of the VOR is produced through an elementary 3 neuron reflex
arc, and is characterised by short latency and high fidelity at frequencies up to
20Hz. However, single cell responses of Medial Vestibular Nucleus (MVN) neurons become
non-linear and distorted for inputs greater than 12Hz, and a homogeneous population
becomes highly synchronised when a common input is applied, and so neither can adequately
encode the required information. It has therefore been theorised that an asynchronous
population is required to achieve the necessary wide frequency response of the VOR
[1].

We use previously published, compartmental models of (A & B subtype) MVN neurons [2] incorporated into the NEURON Simulation Environment to investigate the affect of
noise and heterogeneity in producing and maintaining asynchronicity of the population,
and their affects on the fidelity of response produced by the population (see Figure
1). We provide results from 2 stages of simulations: a 1st stage utilizing a current
injection as an abstraction of both the common input to the population, and the variance
in spontaneous (or 'pacemaker') activity in the population; and a 2nd stage in which
we model synaptic input as the common input to members of the population, and model
heterogeneity through variance in the density of mechanisms responsible for the spontaneous
activity of the neurons across the population. These simulations are performed over
a range of input frequencies and amplitudes.

Figure 1. Population responses for homogeneous & noiseless MVN population (Model 0), and heterogeneous
& noisy population (Model1) for an input of 50pA at 12Hz, produced by current injection.

It is shown that a heterogeneous population, where each member shows a different rate
of spontaneous activity, produces a response with greater fidelity than a homogeneous
population. In addition, different distributions of variability in spontaneous activity,
different input amplitudes, and different intensities of noise, show different response
fidelities, suggestive of a form of optimization in the MVN populations.